Piston assembly for axial type hydrodynamic machines



W. FERRIS May 19, 1953 PISTON ASSEMBLY FOR AXIAL TYPE HYDRODYNAMIC MACHINES 6 Sheets-Sheet 1 Filed Jan. 24, 1952 On I QV/////A/// I:

/ lllia INVENTOR WALTER FERRIS ATTORNEY /Az//// 7/A7 r/ 6 Sheets-Sheet 2 W. FERRIS mm mm ow //x/ //////V/ 2.

PISTON ASSEMBLY FOR AXIAL TYPE HYDRODYNAMIC MACHINES May 19, 1953 Filed Jan. 24, 1952 INVENTOR WALTER FERRIS ATTORNEY May 19, 1953 w. FERRIS 2,638,850

PISTON ASSEMBLY FOR AXIAL TYPE HYDRODYNAMIC MACHINES I Filed Jan. 24, 1952 s Sheets-Sheet 4 INVENTOR.

F 7 BY WALTER FERRIS ATTORNEY W. FERRIS May 19, 1953 PISTON ASSEMBLY FOR AXIAL TYPE HYDRODYNAMIC MACHINES Filed Jan. 24, 1952 6 Sheets-Sheet 5 INVENTOR.

WALTER FERRIS ATTORNEY May 19, 1953 w. FERRIS 2,633,850

PISTON ASSEMBLY FOR AXIAL TYPE HYDRODYNAMIC MACI-IINES Filed Jan. 24, 1952 v s Sheets-Sheet 6 Igl J Rig; .29 .13; Z 8 II f////// J l 3 22 I04 0 INVENTOR. WAL-TER FERRI S- ATTORNEY Patented May 19, 1 953 UNITED STATES QF'FlCE 2,638,850

PISTON ASSEMBLY FOR AXIAL TYPE- HYDRODYNAMIC MACHINES Walter Ferris, Milwaukee, Application January 24, 1952, Serial No, 267,979 22 claims. (Cl. roeita) This application is a continuation in part or application Serial No. 711,674 filed November 22, 1946. a The invention relates to axial type hydrody namie machines which will iunction as pumps when driven mechanically and will function as motors when supplied with liquid under pressure. For the purpose of illustration, the machines will be referred to herein as pumps but it is to be um derstood that the invention is equally applicable to niotorsi i More particularly, the invention relates to piston assemblies for pumps of the type in which a plurality of cylinders are arranged in a cylinder barrel parallel to each other and at equal radii from its axis, a piston is fitted in each cylinder, and each piston is connected by a rod to a thrust member which is driven by a drive shaft and causes the pistons to" reciprocate in their cyl inders.

, The invention is applicable to a number of types of pumps of the above general type. For example, the pump may be of the well known swash plate type in which the cylinder barrel is rotated by a coaxial drive shaft and the thrustmember or swash plate is inclined to and driven by the drive shaft, it may be of the well known angle type in which the thrust member is "normal to and driven by the drive shaft and thecylihder barrel is inclined to and driven from the drive shaft, or it may be of the well known wabble pl te type in which the cylinder barrel is stationary and the thrust member or wattl plate is oscillated or wa'bbled by a member which is inclined to the cylinder barrel axis and is rotated by the drive shaft. it is onl necessar that the pump be of such a type that given point on the face of thethrust member moves toward and L'rhe "cylinders and pistons are alwa arranged in a circle but, due to the plane of the thrust member being inclined to the cylinder barre1 .axis, the extended centerlihcs of the pistons intersect the plane or the thru t member in an ellipse inarranged. The outer end of each piston rod has a, gyiating motion about the piston axis as the cylinder barrel or the wabble plate rotates, thus .sem'pehsating' for the difference between this ,2 radius of the cylinder circle and the majorv and minor axes of the above described ellipse on the plane of the thrust member.

In the prior pumps, each piston rod ordinarily has its outer end connected to the thrust member by a ball and socket joint and its inner end con nected to the piston by another ball and socket joint which is arranged within the piston jar enough from the outer end thereof to cause the pumping forces transmitted from the thrust member through the rod to be, applied to the piston at a point which is intermediate the ends of the cylinder in all positions of the piston. As the outer end of a iston rod gyrates, the ball on the inner end of the rod rotates, in its socket through a limited angular distance and; in order to prevent the inner ball and/or its socket from being abraded by the relative movements thereof; means are provided for lubricating the joint.- This is ordinarily accomplished by drilling a small hole from the inner end of the piston through the socket so that the pressure created in the cylinder forces liquid to flow through the hole and spread laterally between the mating surfaces, thus providing a lubricating film between the inner ball and its socket.

When the pump is in operation, the thrust member forces each piston inward during one half of each revolution of the cylinder barrel and draws the piston outward during the other half or each revolution. Eachinward moving piston ejects liquid from its cylinder and, when the ejected liquid meets a resistance, pressure is created in the cylinder. The force required to create this pressure is equal to the cross-sectional area of the piston multiplied by the unit pressure and, since this force must be transmitted through the inner ball and socket joint, it must not exceed the bearing value of the lubricating film in that joint as otherwise the film would break down and abrasion of the joint would occur.

The bearing area of the inner ball is necessarily only a fraction of the piston area for the reason that the ball is inside of the piston. Therefore, the pressure created by the piston must not errced a given low value for the reason that the foroehecessary to create a high pressure over the relatively large piston area would break down the lubricating film in the relatively small area etween the ball and its socket and would thus cause abrasion oi the ball and socket joint. I l

The present invention has as an object to pro vld a piston a's's'ifibly which when incorporated a machine will enable the machine to operate at pressures greatly in excess 3 of the pressures at which prior machines of the above described types could operate.

Another object is to provide novel means for enabling the thrust member to retract the piston.

Another object is to provide a piston assembly having its rod connected to the thrust member by a ball and socket joint and novel means for lubricating the joint.

Other objects and advantages will appear from the description hereinafter given of piston assemblies in which the invention is embodied.

According to the invention in its principal aspect, the inner end of the piston rod engages a bearing surface on the end wall of a bore formed in the piston instead of the rod being connected to the piston by a ball and socket joint as is the case in the prior pumps of this general type. Neither the bearing surface nor the end of the rod requires lubrication. Consequently, the force which can be transmitted from the thrust member to the piston is limited only by the bearing value of the metal. The pistons may be retracted either mechanically or hydraulically.

The invention is exemplified by the piston assemblies shown somewhat schematically a in the accompanying drawings in which the views are as follows: Fig. 1 is a vertical longitudinal section through a part of a pump having incorporated therein a piston assembly in which the invention is embodied and which is retracted mechanically.

Fig. 2 is a longitudinal section taken through the piston assembly shown in Fig. 1 but drawn to a larger scale.

Figs. 3, 4, 5 and 6 are longitudinal sections I through other piston assemblies which embody the invention and which are retracted mechanically.

Fig. '7 is a diagram showing a thrust member tilted to a greatly exaggerated angle and piston rods connected to the thrust member upon a cir-, cle having a radius greater than the radius of the circleupon which the pistons and cylinders are arranged.

Fig. 8 is a diagram illustrating the relative positions of the outer and inner ends of the piston rods at different points in a cycle of operations and with the thrust member in the position shown in Fig. 7 and in two other positions, the plane of the diagram being indicated by the line 8-8 of Fig. 7. I

Fig. 9 is a'diagram similar to Fig. 7 but showing the piston rods connected to the thrust member upon a circle having a radius less than the radius of the circle upon which the pistons and cylinders are arranged. r Fig. 10 is a diagram similar to Fig. 8 but taken in' the plane indicated by the line Ill-4 ll of Fig. 9. I Figs. 11 and lzare diagrams each of which illustrates two positions of a piston rod relative to the piston with which it is associated, the diagrams being greatly disproportioned.

Fig. 13 is a longitudinal section through a part of a pump in which the pistons are retracted hydraulically, the lower half of the view being in a plane which is inclined to the plane of the upper half in order to show the piston which is' most nearly opposite the piston shown in the upper half of the view.

- Fig. 14 is a circuit diagram showing a pump connected to a'motor in a closed hydraulic circuit and provided with means for supercharging it so that its pistons are retracted hydraulically.

For the purpose of illustration, embodiments of the invention have been shown in Figs. 1 and 4 13 as being incorporated in pumps of the swash plate type such as shown in Patent No. 1,044,838 but it is to be understood that embodiments of the invention may be incorporated in other types of axial pumps.

Figure 1 As shown, the pump has a cylinder barrel I fixed for rotation with a drive shaft 2 and provided witha plurality of cylinders 3 which are equally spaced around shaft 2 and are parallel to the axis thereof, only one cylinder being shown. A piston 4 is fitted in each cylinder and connected to a swash plate 5 which is inclined to the axis of cylinder barrel 1 when the pump is pumping liquid.

Swash plate 5 includes a tilting box 6 which is pivoted upon trunnions not shown, an annular thrust member I which is rotatably supported in box 6 by a bearing 8, and a universal joint 9 which connects thrust member I to shaft 2 so that thrust member I- and cylinder barrel I are rotated in unison by shaft 2.

Each cylinder 3 has a port It] extending from the inner end thereof through the rear end of cylinder barrel I and controlled by a stationary valve II which has two crescent shaped ports I2 formed in the face thereof, only one valve port being shown. Each cylinder port I0 registers with the two valve ports I2 alternately as cylinder barrel I rotates.

When swash plate 5 is inclined to the axis of cylinder barrel I and shaft 2 is driving cylinder barrel I and thrust member I, each piston 4 will be moved outward and will draw liquid into its cylinder 3 through one valve port I2 and its cylinder port Ill during one half of each revolution of cylinder barrel I and it will be forced inward by thrust member I and will eject liquid from'its cylinder 3 through its port In and the other valve port l2 during the other half of each revolution of cylinder barrel I.

Figure 2 In this figure, a piston assembly has been shown connected to a thrust member 1 which may be the thrust member shown in Fig. 1 or it may be a different type of thrust member as explained above.

Motion is transmitted from thrust member I to piston 4 through a piston rod I5 having a spherical head 16 fixed to or formed upon its outer end and fitted in a complementary socket I! which is fixed to thrust member I in any suit-v able manner. As shown, socket H has a cylindrical extension I8 formed thereon and closely fitted in a bore I9 in thrust member I in which it is retained by a pin 20.

Suitable means are provided for retaining head IS in engagement with socket II. As shown, an annular socket. 2| having an inner spherical sur face complementary to the surface of head I6 is urged against head I B by a flanged nut 22 which is threaded upon socket l1. Suitable yielding or spring means, such as a stack of Belleville washers 23, is preferably arranged between socket 2| and the flange of nut 22.

Piston rod I5 extends into a bore 26 which is formed in piston 4 and is enough larger in diameter than rod I5 to permit the outer end of rod I5 to'move radially within bore 26 such as by making bore 26 larger at its outer end than at its inner end, the taper of the bore being exaggerated in the drawing. The inner end of piston rod I5 has a diameter almost as great as andthe inner end portion of rod 15 may be larger,

ndiaineter than the intermediate portionof the rod;

The inner normal to the axis of piston 4 and provides a substantially flat bearing surface 21 which is engaged by a mating bearing surface 28 formed on the end of the rod and normal to the centerline of the rod. Surface 23 may be either flat or spherical. If surface 28 is flat, its outer peripheral edge should be chamfered or rounded in order to avoid any danger of the edgech'ipping off when only a portion of the extreme edge is in contact with surface 21 and a'large pumping force is being transmitted from rod 15 to piston 4, the chamfer being exaggerated in the drawing.

Suitable means are provided for firmly holding surface 21 against surface 28. As shown, a tail rod 29 is fixed to or formed integral with the inner end of piston rod I and extends through an opening 36 which extends from bore 26 through the end of piston 4. A spherical seat 3| is formed in the end of piston 4 around opening 30 and is engaged by a complementary spherical surface on an annular sealing member 32 which loosely encircles tail rod 29. Sealing member 32 is engaged by a sleeve 33 which is slidable upon tail rod 23 and'urged against member 32' by suitable spring means such as a stack of Belleville washers 34 arranged between sleeve 33 and a nut 35 fixed upon tail rod 29.

As the outer end of piston rod it moves radially, tail rod 29 moves about within cylinder 3 and sealing member 32 oscillates upon seat 3| but the angle of movement of tail rod 29 is so small that the parts on tail rod 23 remain clear of the wall of the cylinder in which piston 4 is fitted.

Sleeve 33 is so closely fitted, as by being lapped, on tail rod 29 that it forms therewith a substantially liquid tight joint and the abutting surfaces of sleeve 33, sealing member 32 and seat 3! are so accurately finished that the force exerted by spring means 34 plus the working pressure in the cylinder bore causes them to form substan-- tially liquid tight joints.

However, pressure created in its cylinder by piston 4 during operation of the pump causes a lubricating film to be formed between tail rod 29 and sleeve 33, between sleeve 33 and sealing member 32 and between sealing member 32 and its seat 3! Thispressure also causes a minute flow of liquid from those films through opening 30 into bore 26 but the flow is so minute that it has no appreciable effect upon the volumetric delivery of the pump. The liquid entering bore 26 spreads over surfaces 2! and 2B, the wall of bore 26 and the exterior of rod I5 and not only prevent those parts from rusting but also provides a lubricating film between surfaces 21 and 23 and between the wall of bore 2 6 and the periphery of the inner end portionof rod I5.

The arrangement of the parts is such that, when the outer end of piston rod 15 moves radially in respect to; bore '26 during operation of the pump as explained above, the inner end surface 28'of rod l5 will rock or roll upon bearing surface 21. The peripheral surface of the inner end portion of rod l5 will rub at one point upon the wall of bore 26 but these surfaces: are lubricated, as explained above, so that no abrasion thereof will occur. The inner end surface 28 may also have a very slight radial movement, but such radial movement is so minute that substantially end wall of bore 23 ispreferably 6 no abrasion of surfaces 21 and 28 would occur even if those surfaces were unlubricated.

Since there is substantially no rubbing move ment between surfaces'ZI and 23, it is not necessary to maintain a pressure lubricating film therebetween when piston 4 is creating pressure. Consequently, a very large force equal to the bearing value of the metal may be transmitted through rod l5 to piston 4 so that a pump provided with piston assemblies embodying the present inven-" tion is capable of creating pressures greatly in excess of the pressures which the prior pumps of the same general type could create.

dead 13 of piston rod 4 makes a rubbing contact with socket l! and must be lubricated but, since head it is located outside of the cylinder, it may be made of such size that the area of the lubricating film between it and socket ll is ample to transmit sufficient force to create the desired high pressure in cylinder 3.

Lubrication of head It? may be accomplished inany suitable manner. As shown, a duct 38 extends entirely through tail rod 23, piston-rod l5 and head it into communication with a circular recess 3? which is concentric with the axis of piston rod is and has a diameter less than the diameter of piston 4. Recess 3'! has been shown as being produced by forming a circular counterbore in head ill but it may be produced by forming a flat surface or a convex surface on head. 16. "When piston ii is creating pressure in the cylinder in which it is fitted, such as cylinder 3, liquid will flow from the cylinder through duct 36 to socket H and form a lubricating film between it and. head it The working pressure will extend into recess 3? and into the lubricating film but there will be no pressure in recess 3? or in the film when,

a diameter greater than piston 4 is cut around head It in a plane normal to the axis of piston rod l5 and a drain duct 33 is extended from groove 3% outward through head it to permitv liquid to escape freely from groove 38. Pressure is thus limited to the area between recess 31 and groove 38 and the film in this areamay be designated as a pressure lubricating film but there is no pressure in the lubricating film between head it and the outer part of socket l'l nor in the lllblir cating film between head it and socket 2|. v

When piston 4 is creating a working pressure, the liquid in recess 37 will have the same pressure and it will exert a blow-off force equal to the area of recess 37 multiplied by the unit pressure. The liquid in the pressure lubricating film will have a pressure which at the edge of recess 31 is the same as the working pressure andwvhich gradually decreases to Zero at the edge of groove 38 so,

that the. mean pressure in the film is approximately one half of the working pressure. The liq-,

uid in thepressure lubricating film will exert a blow-off force equal to the area between recess 37 and groove 38 multiplied by approximately one half of the unit pressure and the total blow-off force which tends to separate the mating surfaces, of head 86 and socket ll is equal to the sum of the blow-off forces exerted by theliquid in recess 37 and by the liquid in the pressure lubricating film.

The total blow-off force may be somewhat greater than the pumping force as annular socket 2| is capable of overcoming a substantial excess blow-off force but, since the lubricating film between it and head It is not supplied with liquid under pressure, recess 31 preferably is made as large as practicable and groove 38 preferably is so located that the total blow-off force is slightly less than the pumping force, that is, less than the force exerted upon piston 4 by the liquid in the cylinder.

' The pressure lubricating film will flow at a very limited rate from recess 31 into groove 38 and the velocity of the film will be higher adjacent recess 31 than adjacent groove 38 for the reason that the periphery of recess 3'! is shorter than the periphery of groove 38. A variation in the velocity of a stream of liquid ordinarily causes a variation in the pressure of the liquid but the length of the periphery of recess 3'! is equal to such a substantial part of the length of groove 38 that the variation in velocity is not sufiicient to cause any appreciable variation in pressure. Therefore, such variation in velocity may be and usually is disregarded in calculating the blow-off force.

However, no prior pump or motor was provided with a ball and socket joint having a recess of substantial size formed in the ball at the end of the duct which supplies liquid for lubricating the joint nor was the ball provided with any groove such as groove 38 for limiting the area of the joint which was subjected to pressure.

Without a recess of substantial size at the end of the duct, liquid had to fiow into the film directly from the duct, and the distance around the ball at the zero end of the pressure area was many times the distance around the end of the duct so that the velocity of the liquid entering the film from the duct was many times the velocity of the liquid discharged from the film. Such a large variation in the velocity of the film rendered the blow-off force uncertain and unstable.

Further, the ball must have a radius slightly less than the radius of the socket in order to provide room for the lubricating film. Therefore,

unless the ball and socket joint is large enough to provide a lubricating film of sufficient area to enable the film to exert a blow-off force greater than the force exerted upon the piston during high pressure operation, the axial thrust exerted upon the ball at high pressure would force the area of the ball immediately around the end of the lubricating duct against the surface of the socket and thereby pinch off the flow of liquid from the duct to the film with probable metal to metal contact between the ball and socket, particularly as there is no pressure in the lubricating film until there is pressure in the cylinder, and the pressure in the cylinder often rises almost instantly from zero to maximum.

Also, if no pressure limiting groove such as groove 38 is provided in the ball, the liquid in the film will flow from the lubricating duct outward until it escapes at the edge of the socket and it will escape at a more rapid rate along whichever part of the edge of the socket that happens to be nearest to the end of the lubricating duct as the connecting rod gyrates. This causes the lubricating film to vary considerably in width at opposite sides of the ball and the preponderance of force in the wider part of the film to urge the ball against the opposite side of the socket so that the ball is not centered in the socket and the center of the blow-off force is offset considerably from the connecting rod axis.

In a piston assembly constructed according to the present invention, the large recess 31 provides a definite area which is subjected to the full working pressure and the groove 38 limits the pressure lubricating film to a definite and constant area so that the total blow-off force is definite and always proportional to the working pressure, the groove 38 provides release of film pres sure at a definite and uniform distance from recess '31 so that the change in film velocity is uniform, and the distance between the edge of recess 31 and the edge of groove 38 is relatively short so that the change in film velocity is the smallest possible.

Figure 3 The piston assembly shown in this figure is substantially the same as the assembly shown in Fig. 2 except that it has different means for holding the piston in engagement with the piston rod and for directing lubricating liquid to the head of the piston rod. Therefore, like parts have been indicated by like reference numerals.

The piston assembly includes a piston 4" having a tapered bore 26 extending inward from its outer end and separated by a partition 40 from a bore 4| which extends inward from the inner end of the piston. Motion is transmitted from thrust member I to piston 4 through a piston rod 15 which extends into bore 26 and has a bearing surface 28 on its inner end to engage a bearing surface 2'! on partion 40. Piston rod I5 is connected to thrust member 1 by a ball and socket joint which is identical to the ball and socket joint shown in Fig. 2.

Liquid for lubricating the ball and socket joint is supplied thereto through a small diameter tube 42 which also functions to hold surfaces 21 and 28 in contact with each other so that piston rod It: can pull piston 4 outward on a suction stroke. I

Tube 42 extends from recess 3! through ball I6, an axial bore 43 in piston rod li opening 30 in partition 40, bore 4| and a plug 44 which closes the end of piston 4 to prevent the pressure created by piston 4 from extending into bore 4|. Plug 44 may be provided with an 0 ring packing 45 to form a liquid tight seal between plug 44 and the wall of bore 4|. Opening 30 and a portion of bore 43 are larger in diameter than tube 42 in order to permittube 42 to deflect freely when the outer end of piston rod- 15 moves radially in respect to the cylinder as previously explained.

The rear end of tube 42 is closely fitted in plug 44 and it is rigidly secured thereto as by soldering or by having its end flared. The other end portion of tube 42 is also closelyfitted in and rigidly secured to ball l6. In order thatth outer portion of tube 42 may be initially secured in position, a transverse opening 47 is formed in piston rod l5 at the outer end of bore 43 so that a ring of solder may be placed around tube 42 as will presently be explained.

When surface 28 rocks or rolls upon surface 21 during rotation of the cylinder barrel as previously explained, the rocking or rolling motion of surface 28 will cause a variation in the distance between ball Hi and piston 4 and thereby cause a slight variation in the axial length of tube 42. This variation in axial length is pro vided for by forming a rear portion of tube 42 into a helix 48 the coils of which will yield dur- In order to firmly maintain bearing surface 21 in contact with bearing surface 28 and at the same time to permit surface 28 to. rock or roll upon surface 27. a sleeve 49 is closely fitted upon tube 4'2 in contact with the adjacent coil of helix, t8 and suitable spring means such as a stack of Belleville washers 50 is interposed be.- tween sleeve 59 and the rear face of partition. 50. I When a pump is operating, a lubricating film of liquid is formed between each piston and the wall of its cylinder, and leakage from this film is utilized for lubricating bore 2% and the inner portion of rod I As shown, a hole 52. is formed in the wall of bore 4| at a, distance from the end of piston 4* so thatliquid can flow from the fihn through hole 52, bore 41 and opening into bore 26 where it will spread over the surfaces of bore 25' and rod 15 as explained in connection with the piston assembly shown in Fig. 2. Since this liquid is obtained solely from the lubricating film between the piston and; the wall of its cylinder, the flow of liquid into bore 26 is so minute that it has no appreciable effect upon the volumetric delivery of the pump.

As previously explained, it is not necessary to maintain a pressure lubricating filmbetw'een surfaces '2? and 28 when the piston is creating pressure. Therefore, a very large force equal to the bearing value of the metal may be transmitted through the rod to the piston and cause it tocreate a pressure far in excess of any pressure heretofore possible in pumps of the same general type.

Assembly may be effected by placing sleeve 49 and washers 50 in position upon tube c2 and then passing tube- 42 through opening to. Plug M may then be placed over the rear part of tube 2 and into bore 4i and fixed in position. The rear part of tube 42 may then be rigidly secured to plug 44 to form a liquid tight joint therewith.

Piston rod it may then be placed. over the outer part of tube 42 and moved into bore 26 until surface 28 engages surface 21. The outer portion of tube 42 is initially made longer than the desired length so' that it will protrude beyond head is and sufficient force may be applied to the protruding end portion of-tube -42 to put enough tension in washers 5%] to enable them to hold surfaces 2'! and 2B in contact when piston 4* is pulled outward on ton rod l5.

'Then a ring of solder 5i may be placed around tube 42 in contact with the wall of opening ll and melted in that position as by directing the thereof;

' Figures! 4 The piston assembly shown in this figure olii-. fers from those shown in Figs. 2 and 3 in that theparts of the ball and socket joint are reversed and the piston is pulled outward on a suction stroke by the outer part of the ball and socket joint instead of by the ball. I

,As shown, the pistonassembly includes a piston 4 having a tapered bore 25 extending inward from its outer end and providin upon the end wall thereof a substantially flat bearing surface 211'. A piston rod it extends into bore 26 and has a bearing surface 23 arranged upon its inner end and in contact with surface 27. The

a suction stroke by pis ill outer end of piston rod; ta is provided with, a spherical socket to engage the complementary surface of a ball 56 which is fixed to a thrust member I suchas by having a shank 51 fixed thereto and fastened in thrust member I by a pin 58. Thrust member '5 has been indicated as being the thrust member of the pump shown in Fig. l but it may be the thrust memberof any other pump of the general type mentioned above.

In order that piston 4 may be pulled outward on a suction stroke, an annular spherical socket 59 is fitted upon ball 56 and provided with a cylindrical extension Bil which encircles socket 55' and. the outer end portion of piston 4 An annular member 65' is fitted in extension 60 around piston 4 and is retained in position by a snap ring 62 which is fitted in a groove 63 formed in the inner peripheral surface of extension 6!}. Annular member 55 is engaged by suitable spring means $5, such as a stack of Belleville washers, arranged between it and a pcripheral flange 66 formed upon the end of piston 4 Annular member BI is bored to slip freely over piston 4' and the inner wall of its bore is rounded to permit extension 50 to tilt relatively to piston d as ball H3 moves relatively to the piston axis during operation of the pump. Spring means has sufiicient strength to hold socket 55 against ball 55 and surface 27 against sur-'- face 28 while permitting surface 28 to rock or roll upon surface 2! as ball 55 moves relatively to the piston axis during operation of the pump.

Socket 55 communicates with a bore 61 which extends axially through rod I5 and communicates with an axial bore 68 which extends from bore 26 through the inner end of piston A so that liquid may flow from the cylinder in which piston 4 is fittedthrough passages 88 and! to socket 55 and form a lubricating film upon ball 56. Pressure is transmitted to this lubricating film only when there is pressure in the cylinder of piston 4 A recess 69, which corresponds to the recess 3'! of Fig. 2, is formed in socket 55 around the end of bore 6'! and a pressure limiting groove 10, which corresponds to the groove 38 of Fig. 2, is formed in socket 55 at the proper distance from recess 69 and communicates with a discharge duct H. Recess i9 and groove To perform the same functions as recess 31 and groove 38, and they enable the ball and socket joint to have the same advantages as the ball and socket joint.

Y shown in Fig. 2.

' Leakage of liquid from passages 61 and 68 into bore 26 is substantially prevented by an 0 ring packing l2 which is arranged around surface 28 and is compressed to greater and lesser extents as surface 28 rocks or rolls upon surface 27. Enough liquid to prevent rusting and abrasion of rod lb and the wall of bore 26 may seep past packing H but piston Al has been shown as having a hole 13 extending through the wall of bore 26 to permit minute flow of liquid into bore 26 from the lubricating film between piston 4 and the wall of its cylinder. This flow is so minute that it has no appreciable efiect upon the volumetric delivery of the pump.

As previously explained, it is not necessary to maintain a pressure lubricating film between surfaces 27 and 23 when the piston is creating pressure so that the rod can transmit to the piston a very large force equal to the bearing value of the metal constituting surfaces 2'? and 28 and thereby enable the piston to create pressures greatly in excess of the pressures which prior pumps of the same general type could create.

stantially the same as the piston assembly shown in Fig. 3 except that the helix in the lubricating tube and the spring means for holding surfaces 21 and 28 in contact are arranged within the outer end of the piston rod instead of being arranged within the inner end of the piston. Consequently, like parts have been indicated by like reference numerals and corresponding parts have been indicated by corresponding reference numerals with the exponent added to the reference numerals applied to the piston assembly shown in Fig. 5. Also, the piston assembly is shown in the position occupied when it is at or near the end of its in-stroke instead of near the end of its out-stroke as in the piston assembly shown in Fig. 3.

The piston assembly includes a piston 4 having a bore 26 extending inward from its outer end and providing a bearing surface 21 which is engaged by a bearing surface 28 formed upon the inner end of a piston rod l5 which extends into bore 26 and has its outer end enlarged and provided with a recess 15.

The enlarged outer end of rod [5 is fitted in a recess 16 formed in a ball I6 which is rigidly secured to rod as by being pressed thereon or by being fixed thereto as by soldering or brazing. Ball [6 forms a part of a ball and socket joint which is carried by a thrust member 1 and is identical to the socket shown in Fig. 3 so that a description thereof is deemed unnecessary, ball |6 being provided with a recess 31, a pressure limiting groove 38 and a drainage duct 39 as explained in connection with Fig. 2.

Liquid for lubricating the ball and socket joint is supplied thereto through a small diameter tube 42 which also functions to hold surfaces 21 and 28 in contact with each other so that rod l5 can pull piston 4 outward on a suction stroke.

Tube 42 extends from recess 31 through ball |6, recess 15 and an axial bore 43 which extends from recess 15 through the inner end of rod l5 and from bore 26 through the inner end of piston 4, a portion of bore 43 intermediate the ends thereof being enlarged to permit tube 42 to deflect as surface 28 rocks or rolls upon surface 21. The ends of tube 42 are rigidly secured to ball 6 and to the inner end of piston 4 in a manner to form substantially fiuid tight joints therewith, such as by soldering or by flaring the ends of the tube.

Any pressure prevailing in the cylinder in which piston 4 is fitted will cause liquid to flow through tube 42 to the ball and socket joint to lubricate the same. Recess 31, groove 38 and duct 39 enable the ball and socket joint to have the same characteristics and advantages as the ball and socket joint shown in Fig. 2.

When surface 28 rocks or rolls upon surface 21 during rotation of the cylinder barrel as previously explained, the rocking or rolling motion of surface 28 will cause a slight variation in the distance between ball l6 and piston 4 and thereby cause a slight variation in the axial length of tube 42. This variation in axial length is provided for by forming a helix 48 in that portion of tube 42 which is within recess 15. The coils of the helix will yield during axial movement of piston 4 relative to ball I 6.

In order to firmlymaintain surface 21 in contact with surface 28 and at the same time to permit surface 28 to rock or roll upon surface 21, a sleeve 49 is fitted upon tube 42 in contact with the adjacent coil of helix 48 and suitable spring means 58 is interposed between sleeve 49 and the end wall of recess 15.

As previously explained, it is not necessary to maintain a pressure lubricating film between surfaces 21 and 28 when the piston is creating pres-.- sure. Therefore, a very large force equal to the bearing value of the metal may be transmitted through the rod to the piston and cause it to create a pressure far in excess of any pressure heretofore possible in pumps of the same general type. However, liquid should be admitted to bore 26 to provide lubrication and to prevent rusting. This may be accomplished by forming in the Wall of bore 26 a hole 52 through which liquid may flow at a minute rate from the lubricating film between piston 4 and the wall of its cylinder.

Figure 6 The piston assembly shown in this figure differs from that shown in Fig. 4 primarily in that the liquid for lubricating the ball and socket joint does not fiow through the piston and the piston rod. Also, the piston assembly is shown in the position occupied when it is at or near the end of its in-stroke instead of at or near the end of its out-stroke as is the piston assembly shown in Fig. 4.

As shown, the piston assembly includes a piston 4 having a bore 28 extending inward from its outer end and providing upon the end wall thereof a substantially flat bearing surface 21. A piston rod [5 extends into bore 26 and has a bearing surface 28 formed upon its inner end and in contact with surface 21. The bearing surface 28 on rod I 5 and also the bearing surfaces 28 on the rods shown in the other figures may be flat but preferably are spherical as will presently be explained. It is not necessary to maintain a pressure lubricating film between surfaces 21 and 28 when piston 4 is creating pressure but liquid should be admitted to bore 26 to provide lubrication and to prevent rusting. This may be accomplished by forming in the wall of bore 26 a hole 52 through which liquid may fiow at a minute rate from the lubricating film between piston 4 and the wall of its cylinder.

Piston 4 and piston rod 15 are connected to a thrust member 1 by a ball and socket joint having a ball which is fixed to thrust member 1 and a spherical socket 8| which engages ball 80 and is fixed to the outer end of rod l5. Ball 88 is also engaged by an annular spherical socket 82 having a cylindrical externally threaded extension 83 which encircles ball 80 and socket 8|. Extension 83 has threaded thereon a cylindrical cap 84 having an internal annular spherical surface formed thereon and in engagement with a complementary surface formed upon a collar 85 which is slidable upon piston 4. Suitable spring means, such as a stack of Belleville washers 86, is arranged between collar 85 and an annular flange 81 which is formed upon the end of piston 4.

The arrangement is such that spring means 86 holds socket 8| firmly in engagement with ball 80 and surface -21 firmly in engagement with surface 28 while permitting surface 28 to rock or roll upon surface 21 and thereby vary the distance between piston 4 and ball 80 during radial movement of ball 80 relative to the piston.

- Since a piston might sometimes tend to stick in its cylinder so that retraction of the piston would require considerable force, it is desirable that the ball and socket joint be able to exert a positive force upon the piston. This may be accomplished by providing positive stops which limit the compressibility of the spring means in the ball and. socket joint but preferably the spring means is a stack of Belleville washers, which may be adjusted to have a limited compressibility, or a coiled spring compressed almost to solid position. v

In the piston assembly shown in 6, cap

84 may be screwed onto extension 83 until the Belleville washers are flat so that the stack is substantially solid and then cap 8.4 may be retracted until the stack of washers has just a little more compressibility than is necessary to compensate for the variations in the distance between surface 2'! and ball 80. After the compressibility of spring means 85 has been adjusted, cap 84 maybe locked in its adjusted position as by means of a spring detent 88 which encircles cap 84-and has an end thereof extending into one of aplurality of notches 89 which are formed in annular socket 82.

In each of the piston assemblies shown in Figs. 2, 3 and 5, spring means 23 may be similarly adjusted by. turning nut 22 and, in the piston assembly shown inFig. 4, spring means 85 may be similarly-adjusted by properly locating groove 63'.

Liquid for lubricating the ball and socket joint is supplied thereto through a duct 90 which extends through thrust member I and ball 80. Duct 90 is supplied with liquid in any suitable manner such as in the manner illustrated and described in my co-pending application Serial No. 777,794; filed October 3, 194.7, the piston rod assembly shown in Fig. 6 being primarily intended for use in a pump of the type shown in that application. It is deemed sufiicient to state herein that pump pressure extends through duct Ell to the ball and socket joint only during the time that piston i is creating pressure, and that socket BI is provided with a recess I59, a pressure limiting groove I and a drainage duct II which enable the ball and socket joint to have the same characteristics and advantages as the ball and socket joint shown in Fig. 2.

Figure 13 The pump shown in this figure is similar to the pump shown in Fig. 1 but it difiersprimarily therefrom in that its pistons are retracted hydraulically instead of mechanically. As shown, the pump includes a cylinder barrel IGI which is fixed for rotation with a drive shaft I02 and has formed therein a plurality of cylinders each of which includes an inner pumping portion I63 and an. outer concentric portion I-M of slightly greater diameter. Cylinders Illa-404 are arranged in a circle around shaft I02 and are parallel to the axis thereof.

Each cylinder portion I03 communicates at itsrear or inner end with a passage I 65 which can tends therefrom through the rear end of cylinder barrel II. The flow of liquid to and from cylinder portions I03 is controlled by a non-rotatable: flat valve Hill which engages the rear end of cylinder barrel. Ill! and has formed therein two arcuate ports III! with which each passage Hi communicates alternately as cylinder barrel we rotates, only one valve port IIlI: being shown.

Each cylinder Nit-HM contains a piston hawing an inner pumping portion I08, which is closely fitted for reciprocation in cylinder portion I03, and an outer concentric portion I09 which is closely fitted for reciprocation in cylinder portion I04 and forms with piston portion I08 a shoulder Ilil against which liquid acts to move piston I08-Iil9 outward as will presently be explained.

Inward movement of the pistons is effected by a swash plate 5 which is the same as the swash plate shown in Fig. 1 and the parts thereof have been indicated by the same reference numerals. Swash plate 5 includes a tilting box I5 which is pivoted upon trunnions not shown, an annular thrust member I which is rotatably supported in box 6 by a bearing 8, and a universal joint 9 which connects thrust member I to shaft I02 so that cylinder barrel Illl and thrust member I are rotated in unison.

Each piston IIl8IIl8 has a bore III extendin into it from its front end to receive a piston rod I5 which, with the exception that it does not have a tail rod, is the same as the piston rod I5 shown in Fig. 2 and it is connected to thrust member I by a ball and socket joint I6-22 which is the same as the ball and socket joint shown in Fig. 2. Consequently, like parts have been indicated by like reference numerals so that further description thereof is not necessary. The end wall of bore III constitutes a bearing surface 2? which is engaged by the surface 28 on the end of the piston rod as previously explained. Piston rod I5 functions in the same manner as the piston rod of Fig. 2 except that it does not retract the piston.

For the purpose of illustration, the means for supplying lubricating liquid to the ball and socket joint through the passage 36 in piston rod I5 has been shown as being the same as that described and claimed in application Serial No. 250,728 filed October 10, 1951. As shown, a bore I I2 extends rearward from surface 2'! and has a tubular piston H3 fitted therein. Bore H2 communicates with cylinder portion Hi8 so that plunger II 2 is urged against the surface 28 on rod [5* by any pressure in cylinder portion I08. The arrangement is such that, when pressure is created in cylinder portion I08 liquid can flow therefrom through bore I I2, plunger H3 and the passage 36 in rod I5 to the ball and socket joint. The area of the end of plunger H3 in contact with surface 28 is reduced to a minimum, by chamfering, so that the amount of liquid which can escape from between plunger I I3 and surface 28 is negligible but sufli'cient to provide a protective coating on rod I5 and on the walls of bore Ill. Plunger H3 is made as small as practical but its size has been exaggerated in the drawing in order to properly illustrate it.

The inner end of each cylinder portion IM is connected by a passage H4 to an annular groove H5 which is formed in shaft I02 so that all of the cylinder portions I'M are connected to each other. One or more passages H6 extend inward from the bottom of groove I5 into communication with a passage Ill which extends axially through shaft Hi2 and has a channel H8 connected thereto.

t5 nel Ht through a check valve I22. Channel IN.

'is'conn'ected by a channel I23 to a'relief valve I24 through which gear pump I9 discharges into reservoir I the liquid pumped by it in excess of requirements. Channel H8 is also connected to channel I23 through an orifice choke I25.

The arrangement is such that, when the pump is started, gear pump II9 will deliver liquid through channel I2I, check valve I22, channel 'II8, passages H1 and H6, groove H5 and passages I I4 to cylinder portions I04 until the inner parts of cylinder portions I04 are completely filled with liquid and then pump I I9 will discharge liquid into reservoir I20 through channels I2I and I23 and relief valve I24 which resists the flow of liquid therethrough and thereby enables pump I I 0 to create a low pressure which acts upon shoulder I i0 and tends to move pistons I08'I09 outward. The resistance of relief valve I24 is such that the pressure created by pump 'I I9 is slightly higher than the pressure which normally is required to move outward the pistons on the low pressure side of the pump.

Since there is lubricating film between each piston and the wall of its cylinder, there will be some leakage into and out of cylinder portions I04 and the passages connecting them to each other. That is, liquid will leak from the portions I03 of each cylinder into the portion I04 thereof when the piston in that cylinder is creating pressure and the amount of leakage will be more when the pressure is high than when the pressure is low, liquid will leak from the portion I04 of each cylinder into the portion I03 thereof when the piston in that cylinder is moving out ward and liquid will leak out of the cylinder barr.

rel from the portion I04 of all the cylinders whenever the pump is in operation.

If the leakage into the cylinder portions I04 exceeds the leakage therefrom, the excess leakage can escape through passages H4, H6 and 1 sure determined by relief valve I24, the liquid ejected by the inward moving pistons from the portions I04 of the cylinders thereof would'be considerably in excess of the liquid which could enter the portions I04 of the cylinders containing outward moving pistons and the excess liquid would attempt to flow through orifice I25 which would cause the pressure in the cylinder portions I04 to instantly rise high enough to enable the liquid to break the sticky piston loose and then the pressure incylinder portions I04 would drop to the value determined by the relief valve I24.

In the description of the piston assembly shown in Fig. 2, it has been explained that the area of recess 31 in the ball I0 of the ball and socket joint and the area of the pressure lubrieating film between ball I 6 and its socket preferably are such that the total blow-ofi force exerted by the liquid in recess 3'5 and in the pressure lubricating film is slightly less than the pumping force. The force required to retract a piston under normal conditions is so small that the additiona1 force required to force the piston inward can readily be transmitted through the lubricating film between ball I6 and its socket but in a. pump having two diameter pistons, the area cating film may be such that the total blow-oil force exerted by the liquid in recess 31 and in the lubricating film is substantially equal to the pumping force as the force exerted upon shoulder I I0 holds ball I6 in its socket. If a piston should stick in its cylinder, the force required to retract it would be increased but the lubricating films in the ball and socket joints on the pressure side of the pump would be capable of transmitting the resultant'increased forces unless the sticking of the piston should be of such an unusual nature that a very large additional force would be required to break it loose in which case the resultant increased forces transmitted through the ball and socket joints on the pres sure side of the pump might cause the lubricating films in those joints to be momentarily squeezed out and theballs to make metal-tometal contact with their sockets but the metalto-metal contact would be only momentary so that damage 'to the joints would not occur.

Figure 14 The piston assemblies shown in Figs. 2-6 are provided with mechanical means for moving the pistons outward in response to rotation of a thrust member. In the pump shown in Fig. 13, the pistons are provided with retraction areas and are moved outward by liquid acting upon those areas. But if a machine embodying the invention is employed as a motor, no separate means are required for moving the pistons outward because the pistons are moved outward .by the motive liquid and are moved inward by the thrust member.

Also, if a pump and a motor are connected into a closed hydraulic circuit and the pump is supercharged, the pump pistons are moved outward by the liquid discharged by the motor. As shown in Fig. 14, a pump I30 and a motor I3I are connected into a closed hydraulic circuitby two channels I32 and I33 which connect the two ports of pump I 30 to the two ports of motor I 3| respectively.

I Liquid for supercharging pump I30 is supplied by a gear pump I34 which may be driven in unison with pump I30 and arranged within the casing thereof according to common practice and as shown, for example, in Patent No. 2,577,242. Gear pump I34 has its inlet connected by channel I35 to a reservoir I36 and its outlet connected' to a branched channel I31 one branchof which is connected to reservoir I35 and hasa relief valve I38 connected therein. The other two branches of channel I 31 are connected to channels I32 and I33 respectively and have two which liquid is returned to pump I30 from motor" I3I. The balance of the liquid delivered by gear pump I34 will be discharged into reservoir I36 through relief valve I38 which will enable gear pump "I34 to maintain in channel Assuming that pump I30 and motor I3I are of V the general type shown in Figs. 1 and 13, that the swash plate of pump I30 is inclined in one direction and that pumps I30 and I34 are running, the thrust member of pump I30 will force the pistons on the'discharge side of the pump I32 or I33; a pressure equal to the resistance of relief valve dially outward from the piston axis as is evident by comparing the several positions B to the corresponding positions A. Therefore, the piston.

rod is always inclined radially outward from the piston axis when the pump is at zero stroke so that the rod does not move relatively to its piston and the contact spot remains stationary.

When the thrust member is inclinedito such an angle that the projection of driving center cirole 95 upon a plane normal to the cylinder bar- --rel axis forms an ellipse 96 having a minor axis :equal to the diameter of piston circle 93, the

connecting rod is inclined to the piston axis at all points except points 1 and 7. The outer end of the connecting rod will be outward from the piston axis at all points except points 1 and 7 and it will be either ahead of or behind the piston axis at all points except points 1, 4, '7 and 10. If surface 28 is spherical and continuous as shown in Fig. 6, the contact spot will move radially outward from the rod axis as the rod revolves from position 1 to position 4 and from position 7 to position 10, it will move radially inward to the rod axis as the rod revolves from position l to position 7 and from position 10 to position 1 and it will also move circumferentially in opposite directions through limited angular distances so that surface 28 rolls smoothly upon surface 2?.

If surface 28 is interrupted at the central portion thereof as shown in Figs. 2-5, a slight bump might occur as the rod approaches each of points 1 and 7 but it would occur at only one particular adjustment of thrust member 1.

However, all bumping may be avoided and surface 28 caused toroll smoothly upon surface 21 even if surface 28 is interrupted at its center by arranging the pistons and cylinders on a circle having a diameter which is either greater than the major axis of ellipse 94 or is less than the minor axis of ellipse 94.

Figures 9-10 These figures are the same, respectively, as Figs. 7 and 8 except that the pistons and cylinders are arranged in a circle 91 which has a diameter greater than the major axis of ellipse '94 so that each piston rod is always inclined inward from the piston axis at every point in a cycle of operations and at all inclinations of the thrust member. Since the rod is always inclined to the piston axis, the contact spot does not approach the rod axis but remains upon spherical surface 28 which will roll smoothly upon surface 21 as the inclination of the rod changes during operation of the pump.

If the pistons and cylinders were arranged upon a circle having a diameter less than the minor axis of ellipse 94, the same result would be obtained but each connecting rod would always be inclined outward instead of inward from the piston axis.

Figures 11 and 12 In these figures the length of a piston rod relative to the diameter of the rod has been reduced to a small fraction of the actual length and the indicated movement of the driving center has been exaggerated in order to prevent certain lines from merging with each other.

It is obvious that the center of the contact spot between bearingsurfaces 21 and 28 will be on the piston rod axis when that axis is coincident with the piston axis, that surface 23 is prevented .by the sidewall of bore 26 from moving an appreciable distance radially of the piston axis,

and that a slight inclination of the rod axis relatively to the piston axis will cause the contact spot to suddenly shift from the center of surface 28 to a peripheral portion thereof if surface 23 is flat.

However, if surface 28 is spherical and the axis of the rod is tilted out of alinement with the piston axis, the center of the contact spot will shift away from the piston axis a distance which is proportional to the radius of surface 28 and the angle between the rod and piston axes.

For example and as indicated in Fig. 11, if surface 28 had a radius RI struck from the driving center and the driving center were shifted from the position C1 of Fig. 8 to the position D1 of Fig. 8, the center of the contact spot would shift from the piston axis to point P1 which is quite close to the piston axis so that the contact spot would move around over a relatively small area.

However, if the driving center were shifted the same distance and if surface 28 had a radius R2 twice the lentghof radius RI as indicated in Fig. 12, the center of the contact spot would shift to a point P2 which is twice as far from the piston axis as is point Pl so that the contact spot would move over a large area of surface 21.

Also, if the cylinder circle had a diameter greater than the major axis of ellipse 94 as shown in Fig. 10 or if it had a diameter less than the minor axis of ellipse 94 so that the axis of each connecting rod would always be inclined to the piston axis as explained above, the contact spot would always be spaced from the rod axis and, if surface 28 had a radius of sufiicient length, the contact spot would remain outward from the lubricating tubes and passages of the piston assemblies shown in Figs. 2-5 so that the surfaces 28 on the rod of those assemblies would at all times have a smooth rolling or rocking contact with the corresponding surface 21.

The invention herein set forth may be modified in other ways and embodied in other forms without departing from the scope thereof. The invention is hereby claimed as follows:

1. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially flat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having a bearing surface arranged upon its inner end and in contact with the bearing surface on said piston, and a universal joint larger in diameter than said piston arranged upon the outer end of said rod for connecting it to said thrust member. Y

2. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating saidpiston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially flat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having a bearing surface arranged upon its inner end and in contact with the bearing surface on said piston, a universal joint larger in diameter than said piston arranged upon the outer end of said rod forconnecting it to said thrust member, and yielding means for retain- 23. thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore, a universal joint connecting said rod to said thrust member and having mating convex and concave spherical surfaces and a recess of substantial area formed between said surfaces upon the axis of said rod, a bearing surface arranged upon the inner end of said rod and in contact with the bearing surface on said piston, channel means for supplying working liquid to said recess to thereby cause liquid to fiow between said mating surfaces and form a lubricating film therebetween, and means for limiting the area into which pressure can extend from said recess into said film comprising an annular groove formed in one of said surfaces at a predetermined distance from said recess and means for permitting free escape of liquid from said groove, the diameter of said groove being greater than the diameter of said cylinder and said recess being large enough to cause the velocity of the liquid flowing therefrom into said film to be only a small frac tion of what it would be if the liquid flowed into said film directly from said channel means.

10. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat hearing surface on said piston at the inner end of said bore, a piston rod extending into said bore, a universal joint connecting said rod to said thrust member and having mating convex and concave spherical surfaces and a recess of substantial area formed between said surfaces upon the axis of said rod, a bearing surface arranged upon the inner end of said rod and in contact with the bearing surface on said piston, channel means for supplying working liquid to said recess to thereby cause liquid to flow between said mating surfaces and form a lubricating film therebetween, and means for limiting the area into which pressure can extend from said recess into said film comprising an annular groove formed in one of said surfaces at a predetermined distance from said recess and means for permitting free escape of liquid from said groove, the area of said recess and the area between said groove and said recess being such relatively to each other and to the area of said cylinder that the liquid in said recess and the liquid in the film between said recess and said groove when under pressure will exert a total blow-oil force which is not a substantial amount more or less than the force exerted upon said piston by liquid in said cylinder at the same pressure as the liquid in said recess and the blow-off force exerted by the liquid in said recess is a large part of said total blow-01f force.

11. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat'bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having its inner end loosely fitted in the inner end of said bore and provided with an end face to engage said bearing surface, a universal joint having one part thereof fixed to the outer end of said rod and another part thereof fixed to said thrust member, said thrust member causing said connecting rod to reciprocate said piston and. the outer end of said connecting rod to move radially in respect to said cylinder and thereby cause said end face to roll upon said surface during operation of said machine, and means for supplying lubricating liquid to said bearing surface and said end face from the lubricating film which is formed between said piston and the wall of its cylinder during operation of said machine.

12.. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have apiston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore, a universal joint having one part thereof fixed to the outer end of said rod and another part thereof fixed to said thrust member, and a spherical face arranged upon the inner end of said rod to engage said bearing surface and having a radius greater than the distance between said bearing surface and the center of said universal joint, said thrust member causing said piston rod to reciprocate said piston and the outer end of said piston rod to move radially in respect to said cylinder and thereby cause said end face to roll upon said surface during operation of said machine.

13. In an axia1 type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore, a universal joint having one part thereof fixed to the outer end of said rod and another part thereof fixed to said thrust member, a spherical face arranged upon the inner end of said rod to engage said bearing surface and having a radius greater than the distance between said bearing surface and the center of said universal joint, said thrust member causing said piston rod to reciprocate said piston and the outer end of said piston rod to move radially in respect to said cylinder and. thereby cause said end face to roll upon said surface during operation of said machine, and spring means for retaining said face in contact with said surface while permitting said face to roll upon said surface.

14. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having its inner end loosely fitted in the inner end of said bore and provided with an end face to engage said bearing surface, a universal joint having one part thereof fixed to the outer end of said rod and another part thereof fixed to said thrust member, said thrust member caus- Maestro .6 ins; said Aston, 29.; t 'iecinreeate 1,53 .11. eistqn det mined distance iromsaid recess and mean a d t. Ma et s i ll astondaLQJjiQiie for. permitti frag escape Oi liquid m Said xli i eran it d s n sts); 4 tees to roll ne n. .sa on f s m 1 groove e v 7- n an axial tim h dr dyna i machin hav a cy nder barrel pro ide wi h a yl nde ad pted t have a s er; fi h in a d a th ust member for re proe sa d pis n; the qmbinet o Q a1 istes f t ed i ar i cy inde nd hav n bore ex e in i wa d from t outer end thereof, a substantially flat bearing 9 said pistes. at the inner z is ti 19 ton mi e t into sai here and i5. an'axiai y v .v 1 w v N wi aid b re w. i eet is e in eie caie ..'i'i9i .1 A e 9t 8 i 12 ton red s m e 1 ss es t9 cyl nde and t ei 4. a s d e p e tq r 4 ses. and sulfate n f said nga hine, n

iprocate said D saidrod to gw et siiahr in t ente we r .er-sese sa d-1h s; see, a universalzioint hay ng. part thereof. fixed to the outer end of aid, pjst rodandf nether part thereoiifixed W t niembegsaidthrust member causing said piston rodto reciprocate said piston and. th outer 2 d .Q said piston rod to. move radially in fiip 0 said; cylinder and thereby cause said, end k e to roll; upon said surface during operation 0-, said machine, said rods having a passage extending therethrou'gh for c'ondueting liquid from said cylinder to said 'universai'joiiit to; lgleieate the same, a. sphericar'seat"foriried bore, a piston upon the end: at said piston around said tail rod, having its inner end loosely fitted in the inner sealing means larrangedfupon said tail rod and l 9}" s id re and provided with an end; face having a seat 10oinplementary to'the seat on sa d n and socket piston, and spring meansitor holding said seats flit "to said thrust in Contactwitheaichiother and said face in' een: membe-Fand the socket ther'eo fx ed to ijiiter tact with said surface. whilep'erinitting said face endof saidrod and provided tofrolluponisaidsurface" 155 63 sai aid nit-use '19. In: an axial "tyne hydrodynamic machine t id rodto reciprocate sai'd 151$ 4 having 'aiylihder tamer-penned en d off a d rod to move radi in r e sp to inder adapfted to have Whistdn 'fitte'dthei elri said (Cylinder andthereby ca (5 said'eiid'i'aee anda th rust inenrib'e'r ffonr to 1-011 upon said surface during operation of 65 piston, the bemeniation si s piston -tted insaid said machine, spring means for retaining said cylinder and having a tapered bore extending face in contact with said surface while permitinward from the outer end thereof, a substanting said face to roll upon said surface, chantially fiat bearing surface on said piston at the nel means for supplying working liquid to said inner end f aid bor a pi n rod xte recess to thereby cause liquid to flow between i0 into said bore and having its inner end loosely said mating surfaces and form a lubricating film fitted in the inner end of said bore and provided therebetween, and means for limiting" the area W an end face to en Sa d bear u fi into which pressure can extend from said recess a ball and socket joint having the bail thereof into said film comprising an annular groove fixed to the outer end of said rod nd th t, formed in the surface of said socket at a prethereof fixed to said thrust member, said thrust 27 member causing said rod to reciprocate said piston and the outer end of said rod to move radially in respect to said cylinder and thereby cause said end face to roll upon said surface during operation of said machine, a tube for conveying liquid from said cylinder to said ball and socket joint to lubricate the same, and means including said tube for holding said face in contact with said surface while permitting said face to roll upon said surface.

20. In an axial hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having. a bore extending inward from the outer end thereof, a substantially fiat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having its inner end loosely fitted in the inner end of said bore and provided with an end face to engage said bearing surface, a ball and socket joint having the ball thereof fixed to the outer end of said rod and the socket thereof fixed to said thrust member, said thrust member causin said rod to reciprocate said piston and the outer end of said rod to move radially in respect to said cylinder and thereby cause said end face to roll upon said surface during operation of said machine, a tube for conveying liquid from said cylinder to said ball and socket joint to lubricate the same and having its opposite ends fixed to said piston and to said ball respectively to enable said thrust member to move said piston outward of said cylinder, and a helix formed in said tube to compensate for variations in the distance between said piston and said ball as said face rolls upon said surface.

21. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially fiat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having its inner end loosely fitted in the inner end of said bore and provided with an end face to engage said bearing surface, a universal joint having one part thereof fixed to the outer end of said rod and another part thereof fixed to said thrust member, said thrust member causing said rod to reciprocate said piston and the outer end of said rod to move radially in respect to said cylinder and thereby cause said end face to roll upon said surface during operation of said machine, a flange arranged upon the outer end of said piston, a reaction member carried by said universal joint, and spring means arranged between said flange and said reaction member to hold said face in contact with said surface while permitting said face to roll upon said surface.

22. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a substantially flat bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having its inner end loosely fitted in the inner end of said bore and provided with an end face to engage said bearing surface, aball and socket joint having the socket thereof fixed to the outer end of said rod and the ball thereof fixed to said thrust member, said thrust member causing said rod to reciprocate said piston and the outer end of said rod to move radially in respect to said cylinder and thereby cause said end face to roll upon said surface during operation of said machine, a flange arranged upon the outer end of said piston, a collar slidable upon said piston and having a spherical face upon one side thereof, spring means having a limited compressibility arranged between said flange and the other face of said collar to permit said end face to roll upon said bearing surface, and retracting means engaging the spherical face on said collar and a spherical face on said ball to enable said thrust member to retract said piston and being adjustable to vary the compressibility of said spring means.

23. In an axial type hydrodynamic machine having a cylinder barrel provided with a cylinder adapted to have a piston fitted therein and a thrust member for reciprocating said piston, the combination of a piston fitted in said cylinder and having a bore extending inward from the outer end thereof, a bearing surface on said piston at the inner end of said bore, a piston rod extending into said bore and having its inner end provided with an end face to engage said bearing surface, and a universal joint having one part thereof fixed to the outer end of said rod and another part thereof fixed to said thrust member, said thrust member causing said rod to reciprocate said piston and the outer end of said rod to move radially in respect to said cylinder and thereby cause said end face to move upon said surface during operation of said machine and said piston having an opening through the side wall of said bore through which lubricating liquid is supplied to said bearing surface and said end face from the lubricating film which is formed between said piston and the wall of its cylinder during operation of said machine.

WALTER FERRIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 51,056 Isham Nov. 21, 1865 1,044,838 Williams Nov. 19, 1912 1,345,808 Reynolds July 6, 1920 2,141,935 Rose Dec. 27, 1938 2,361,046 Molly Oct. 24, 1944 

